The art has long felt a need for a simple, inexpensive and automatic apparatus for dispensing the contents of a container of liquid in relatively small, accurately measured increments. This need exists, with varying requirements as to accuracy and service conditions, in such widely-varying applications as dispensing of liquid detergents, pouring of alcoholic beverages, dispensing of reagents in chemical laboratories and nutrients in bacteriology laboratories, etc.
One of the most important of such applications is in the dispensing of liquid medications, of both the ethical and the over the counter classifications. Although the dispensing of such medications does not in most cases require an analytical degree of accuracy and reproducibility, the usual approach--typically "one teaspoonful twice a day"--leaves much to be desired, considering that a teaspoonful, which is nominally equivalent to one dram, or 3.53 ml., or to 4 ml., depending on the conversion tables employed, may in fact be from 4 to 7.5 ml., more or less, depending on the design of the "teaspoon" (frequently more properly designated a dessert spoon) employed. In addition, an appreciable error is introduced in the measuring operation, depending on the skill of the person making the measurement. Thus one individual may fail to fill the spoon completely, to avoid spillage, whereas another may actually "pile up" the liquid beyond the rim of the spoon, to ensure "good measure." (Tablespoons vary even more widely--e.g. from 8 to 24 ml. depending on the particular spoon used, vs. a nominal value of 4.times.3.53=14 ml., approximately).
Moreover, the conditions of use may be such that the use of a spoon as a measuring device may be bypassed altogether, e.g. when the medication is to be mixed with water or other liquid, thus eliminating a possible source of inaccurate measurement and possible contamination introduced by possible spillage from a spoon or the like, or the possibility that such spoon or the like is contaminated.
Many devices have been proposed for the dispensing of controlled-volume increments of liquids from containers, but all, while partially successful, have suffered from one or more of a number of disadvantages. For example, many of the proposed expedients have been suitable for dispensing of only one predetermined quantity of liquid. Others have been prone to inaccuracies and erratic operation brought about by differences in pressure between the ambient atmosphere and the vapor space over the liquid inside the apparatus. Thus a partial vacuum inside the container, whether caused by fluctuations in ambient temperature and barometric pressure, or altitude differences between the point where the dispenser is first joined to the container and the point of use, or caused by repeated withdrawals of liquid without replacing the volume thus lost when an equivalent volume of air, tends to resist flow of liquid out of the dispenser, resulting in short dosage. By the same token an excess pressure in the apparatus tends to promote outflow of liquid, tending to overdosage. This difficulty does not arise when the container is opened to the atmosphere to pour out the measured dosage with each use, but this is attended by the danger of spillage and/or atmospheric contamination, as well as changes in potency when the formuation of the medication contains volatile components, such as alcohol, chloroform, ether, etc.
On the other hand, those which were not thus opened for each use generally depended upon providing for pressure equalization by allowing air to bubble into the reservoir of liquid medication simultaneously with the withdrawal of liquid therefrom. This led to the difficulties mentioned above, and also required that the dispenser construction be rather complicated, to allow measured dispensing of the liquid and simultaneous pressure equalization, without sacrificing either objective for the other. Some of these devices even made use of differential air pressure to control the flow of liquid and thereby cut off the flow at the desired volume. Such devices, although highly ingenious in many cases, generally required rather sophisticated, complicated, and consequently expensive mechanical construction.
While the foregoing description of the background of the invention has been touched primarily in terms of dispensing of medication, it will be recognized that the same considerations apply, with varying degrees of emphasis to a wide variety of other applications, as noted above.
Perhaps, one of the most important problems facing the packaging industry today are child safety features. These needed features compel the development of a liquid dispenser that will prevent a child from obtaining access to the contents of the container, while nevertheless enabling aged, infirm or arthritic adults to manipulate the container dispensing mechanism with sufficient ease to permit them to have access to the packaged medicines, materials, cleaning fluids or the like. For a number of years, articles have been published that describe the difficulty of developing a truly satisfactory "child-proof" medicine dispenser or bottle. In this respect the Jan. 9, 1970 issue of "The Kiplinger Newsletter," the May 11, 1978 issue of "The Wall Street Journal" (page 42) and the article entitled "Child-Proof Bottles vs. Five Year-Old- Kids" that was published in the August, 1978 edition of "Family Health" stress the unsolved problem of designing a bottle cap or closure that not only frustrates children's attempts to remove, but also does not make it too difficult for the aged or the weak to manipulate. The most popular commercial bottle caps of this nature all seem to require combinations of motions that often make cap removal very awkward for the elderly. The difficulty in reconciling these two apparently conflicting goals is underscored by the fact the U.S. Government Poison Prevention Packaging Act passed in 1970 seems to be largely unfulfilled in the marketplace for both liquid and solid containers. Thus, in addition to all of the foregoing needs, the further need to provide a liquid dispenser mechanism that does not involve coordination exercises or displays of brute strength to draw correct measures of contents from the bottle or package has heretofore remained unsatisfied.